Fruit flies

Keeping your orchard pest-free. By Dane McDonald.

It is the trouble every fruit grower is trying to avoid— finding a fruit-fly larva— just one hit can ruin the day, if not the entire season.

“Nobody wants a maggot in their apple,” says FruitFly Africa manager Nando Baard, with a smile.

Fruit damage is caused by the fruit-fly life cycle. The female fruit fly lays her eggs under the skin of the fruit, where they hatch. Here the larvae feed on the fruit until they crawl out of the fruit, fall onto the ground, and pupate in the soil. At this stage the fly emerges allowing the life cycle to start again.

At the FruitFly Africa facility, based in Stellenbosch, Baard shares the story about India which had its export market closed down due to the European Union’s (a highly lucrative market) strike system for pests.

“About three years back they had numerous strikes which closed the EU market for them for 18 months,” he says.

According to Baard they needed to reapply for the following season, and if it happens to the South African fruit industry it will be a big problem.

It is estimated that crop losses and control costs as a result of fruit flies in the Western Cape alone amount to (a conservative estimate) of more than R20 million per year, according to Baard.

Economically important fruit flies

In South Africa there are three fruit flies of economic importance: Ceratitis capitata, C. rosa, and C. quilicii, which are of concern to the deciduous fruit industry in the Western Cape.

Dr Minette Karsten who has been working on fruit flies for much of her postgraduate life says the fruit flies have an Afrotropical native range with very little information on the actual origin of the flies.

A recent paper by Karsten and her colleagues listed 14 Afrotropical fruit flies of varying economic importance. Karsten says some of the flies have been in South Africa since before the beginning of fruit cultivation.

In terms of their distribution fruit flies are challenging to map, says Karsten, adding that information is patchy and that global distribution maps do not help at a local level.

In most cases distribution seems to be driven by ambient temperature with C. capitata thriving in dry, hot conditions and C. rosa and C. quilicii faring better in colder conditions and at higher altitudes.

Baard’s colleague and FruitFly Africa field operations manager Elsje Schreuder takes a broader view and says fruit flies are found everywhere especially in home gardens in towns.

Schreuder says the prevalence of fruit flies in home gardens is problematic because despite producers’ best efforts at pest-control activities in orchards, very little control is being carried out in home gardens, towns, and alternative hosts.

Fruit-fly management

Baard says the current management regime for fruit flies in South Africa varies depending on the region and who one speaks to, but mostly it will include monitoring, orchard sanitation and chemical control with some type of fruit-fly bait.

“In the areas where we do area-wide integrated pest management programmes we also do the monitoring. We try to get growers to do better orchard sanitation and we do aerial baiting with GF-120 (a protein bait spray) as well,” according to Baard.

The FruitFly Africa operation incorporates the use of a helicopter and/or fixed-wing aircraft to bait effectively across its grower regions. Baard explains that the attractant is highly concentrated requiring only 1 litre of GF-120 per litre of water per hectare.

In addition, while GF-120 attracts fruit flies it is not harmful to other insects which are not attracted to the bait. The fruit flies are then killed by the active ingredient — Spinosad — an organically certified product which Baard says presents minimal risk to other animals.

The other arm of FruitFly Africa’s activities involves Sterile Insect Technique. At their facility 56 million sterile male Mediterranean fruit flies are bred per week. At the pupal stage the male flies are irradiated rendering them sterile.

These sterile male fruit flies are then released across the relevant fruit-growing areas where they compete effectively with sexually viable males for female mating opportunities leading to pest-population control.

An eye on the future

While Baard and his team are currently effective in their fruit-fly management workflow and receiving significant buy-in from growers across the board, they are keeping an eye on future developments — predominantly biological pest control.

Stellenbosch University entomologist Dr Pia Addison says a few potential biological control organisms have been developed — largely nematodes, fungi, and parasitoids — with nematodes being the most effective option at the moment.

Karsten, who works closely with Addison, says the challenge is finding biologicals that are native to the South African region and developing effective application methods for growers.

“Some of those technologies still have to be developed into products that can be bought off the shelf,” says Karsten.

Chemical heyday over

Karsten says the fruit export market is moving away from harsh chemicals like organophosphates towards more biological options.

“People are becoming much more interested in the fruit-production process and which chemicals are being applied,” she says.

Yet, the fruit-fly fighters on the ground are not quite sure about the current economic viability of using biologicals in isolation.

At the same time Baard agrees with his researcher colleagues. “The markets definitely do not want organophosphates sprayed on their fruits anymore,” he comments. “So, it will be baits, biological control, orchard sanitation, and effective monitoring.”

Image: Mediterranean fruit fly — Ceratitis capitata — is believed to be an introduced pest.

Supplied by Caro Kapp | Blue Bug Diagnostics.